Variational Monte Carlo calculation of n+³H scattering

The quantum Monte Carlo (QMC) methods have a long history of successful bound state calculations in light systems but so far have seen very little application to unbound systems. In this talk we describe a numerical method that improves the efficiency and accuracy of scattering calculations in QMC. We present an initial test case of n+³H using variational Monte Carlo (VMC) wave functions with various two- and three-body potentials, including the Norfolk family of potentials. The method consists of inferring long-range amplitudes in the wave function from integrals over the short-ranged region of interaction. Specifically, we compute spectroscopic overlaps and scattering observables using these integrals and report improvement relative to direct evaluation of the same wave function. Compared with previous QMC scattering calculations, the new method avoids difficulties associated with precise computation of energy differences and with convergence outside the interaction region. It also enables calculation of approximate phase shifts over a range of energies from a single wave function. This initial test-case applies the Norfolk chiral potentials to A>2 scattering, and it paves the way for use with more-precise Green’s function Monte Carlo wave functions.